1. Field of the Invention
The invention relates generally to a safety system for garage door openers and particularly to a light beam obstruction detection system for garage door openers.
2. Description of the Prior Art
Safety systems for a garage door openers which detect the presence of an obstruction to door movement are known in the art. Typically the garage door moves on curved tracks. An electric motor opens and closes the door by means of a driving mechanism. Safety systems are intended to control door movement in response to certain sensed conditions. One such system, disclosed in U.S. Pat. No. 4,922,168, uses a light transmitter and a light receiver which are laterally opposed near the edges of the door opening. The light transmitted is generally infrared. The transmitter and receiver cooperate to detect an obstruction in the path of the transmitted signal. When the obstruction interrupts the signal from the transmitter to the receiver, the controller prevents the door from closing.
There are several problems with the prior art obstruction detectors. The transmitter and receiver are located near the ground at the door opening which exposes them to rain, snow and physical contact from people and objects passing through the door. Such physical abuse can cause the components to malfunction or degrade; thus, more frequent repair and replacement are required. The transmitter and receiver must be in electrical communication with the door operator which is generally located near the ceiling of the garage some distance from the transmitter and receiver. Multiple enclosures must be used which are costly and more difficult to install than a single enclosure. Often, the space for installing the transmitter and receiver near the door is limited making installation difficult if not impossible. Proper alignment of the relatively large enclosures can also be difficult. Costly power and signal conductors must run from the door operator to the transmitter and receiver. Worn insulation on the conductors is a potential safety hazard which can cause system failure resulting from a short circuit.
It would be preferable to have an obstruction detection device which provides simple installation, improved durability and a minimum number of pieces without compromising the reliability or effectiveness of the system.